Welcome to this third installment
in the ongoing MathWorks technical series
on the use of RF Toolbox.
In this installment, we are going
to continue to work with S-parameter Networks.
Specifically, we are going to continue to discuss methods
for network termination using both standard and arbitrary
impedances.
Let's begin by outlining the principal functions that
are going to be used today, namely snp2smp, rfinterp1, x
and cascadesparams.
Again, help for each of these RF Toolbox functions
can be found by typing in help and the function
name at the Matlab command prompt
or typing in the function name in the Help browser.
One RF Toolbox product example that I find particularly useful
for the use of snp2smp is modeling
a high-speed backplane.
This example shows the user how to reduce a 16-port network
to a four-port network by appropriately terminating
12 of the ports in order to create a single differential
channel, useful for signal integrity analysis.
Network terminations can be characterized
by single port S-parameter files.
These single port networks may use different frequency values
from the network being terminated
to describe the one-port impedance behavior.
If this is the case, it will be necessary to define
a common set of frequencies for all elements in the network.
When using RF Toolbox you will need
to use the rfinterp1 function to interpolate the S-parameters
at frequency points in between the original characterization
frequencies.
Once the interpolated S-parameters are determined,
one can use the cascade sparams function
to concatenate arbitrary network parameter files together.
The rfinterp1 function is also very
useful for converting logarithmically spaced
frequency points to linearly spaced frequency points
and vise versa.
Let us now look at an example where we will use
rfinterp1 and cascadesparms.
Let us first look at the frequency range of both
the three-port network and the one-port load that
will be used to terminate the third port
of the three-port network.
You will notice that they have both a different number
of frequency points as well as frequency values.
Since the one-port network has a wider frequency
range than the three port, we will use rfinterp1
on the one-port network and interpolate S-parameters
over the range of frequencies given
for the three-port S-parameter file.
Now that both set of S-parameters
have a common frequency range, they
can be combined to form a single two-port network.
Once this task is completed the reflection
response of each of the ports can be plotted and analyzed.
Now that both sets of S-parameters
have a common frequency range, they
can be combined to form a single two-port network.
Once this task is completed, the reflection response
of each of the ports can be plotted and analyzed.